Don E. Riemenschneider

Weed management in short rotation poplar and herbaceous perennial crops grown for biofuel production

Abstract Weed management is a key element of any crop production system. Weeds are a particular problem in the production of short rotation woody and perennial herbaceous biomass crops due to the shortage of registered herbicides and integrated weed management systems. Herbicides will be an important component of weed management of biomass crops. However, producers should take a broader view of weeds and incorporate all available weed management tactics in these production systems. In both short rotation poplar and herbaceous perennial crops, weed control during the establishment period is most critical. New plantings of these species grow very slowly and do not compete well with weeds until a canopy develops. Effective weed control can double the growth of short rotation poplar crops and affect the variability of the resulting stand. In crops like switchgrass, uncontrolled weeds during establishment can result in stand failure. Cultural practices such as site preparation, using weed-free seed, fallowing, selecting the proper planting dates, companion crops and controlling weeds in previous crops must be combined with herbicides to develop integrated management systems. Weeds may also cause problems in established stands through competition with the biomass crop and by contaminating the product. Effective and economical weed management systems will be essential for the development of short rotation woody and herbaceous perennial biomass crop production systems.

A family of wound-induced genes in Populus shares common features with genes encoding vegetative storage proteins*

Two wound-inducible cDNAs from poplar leaves show sequence identity to vegetative storage proteins (VSP) that accumulate seasonally in poplar bark tissues. We have compared the genomic organization, cDNA sequences and expression of the genes encoding the wound-inducible cDNAs (win4) with that of a bark VSP (called bark storage protein, or BSP). There appear to be several win4 genes in the poplar genome which segregate as a single locus and are therefore likely to be clustered. The same is true of the BSP genes. The win4 locus is linked (map distance of 5 cM) to the BSP locus, consistent with a common evolutionary origin of the genes. A near full-length win4 cDNA shows 75% sequence identity to BSP cDNAs. Both win4 and BSP are systemically wound-inducible; win4 transcripts accumulate in leaves and stems, whereas BSP transcripts accumulate almost exclusively in stems. A phloem transport-dependent signaling mechanism appears to be involved in systemic win4 expression after wounding. In contrast to BSP gene expression, win4 genes are not expressed in response to short day conditions. The data indicate win4 and BSP genes are differentially regulated, and their products may play important roles in the storage and reallocation of nitrogen in perennial plants.

Clonal variation in survival and growth of hybrid poplar and willow in an in situ trial on soils heavily contaminated with petroleum hydrocarbons.

Species and hybrids between species belonging to the genera Populus (poplar) and Salix (willow) have been used successfully for phytoremediation of contaminated soils. Our objectives were to: 1) evaluate the potential for establishing genotypes of poplar and willow on soils heavily contaminated with petroleum hydrocarbons and 2) identify promising genotypes for potential use in future systems. We evaluated height, diameter, and volume after first year budset by testing 20 poplar clones and two willow clones. Unrooted cuttings, 20 cm long, were planted in randomized complete blocks at 0.91- × 0.91-m spacing at Gary, IN, USA (41.5°N, 87.3°W). Four commercial poplar clones (NM6, DN5, DN34, and DN182) were planted as 20- and 60-cm cuttings. Sixty-cm cuttings exhibited greater height and diameter than 20-cm cuttings; however, we recommend continued use and testing of different combinations of genotype and cutting length. We identified promising genotypes for potential use in future systems and we recommend allocating the majority of resources into commercial poplar clones, given their generalist growth performance. However, further utilization and selection of experimental clones is needed. Specific clones rather than genomic groups should be selected based on the geographic location and soil conditions of the site.

Expression of an Herbicide Tolerance Gene in Young Plants of a Transgenic Hybrid Poplar Clone

The herbicide glyphosate (N-phosphono methylglycie) kills plants primarily by inhibiting the enzyme EPSP synthase (5-enolpyruvylshikimate-3-phosphete synthase). The aroA gene codes for EPSP synthase. An altered Salmonella typhimurium aroA gene, which codes for a less susceptible EPSP synthase, was previously enqineered for expression in higher plants, and inserted into hybrid poplar NC-5339 cv. ‘Crandon’ (Populus alba × P. grandidentata) by using an Agrobacterium tumefaciens binary vector.

Development of Glyphosate-Tolerant Populus Plants through Expression of a Mutant aroA Gene from Salmonella Typhimurium

The development of a plant regeneration and transformation system for the poplar hybrid NC5339 (Populus alba x Populus grandidentata) is described. A binary armed strain of Agrobacterium tumefaciens harboring three chimeric gene fusions was used as a vector. Genetic transformation was confirmed through western blot analyses. Employing this system, we have introduced into Populus NC5339 a bacterial aroA gene which confers tolerance to the herbicide glyphosate. Expression of this foreign gene into Populus is discussed.

Screening Conifers for Resistance to Gremmeniella abietina

Seed from 125 seed sources were grown as greenhouse container stock. Seedlings were inoculated with either the North American or European strain of G. abietina. Inoculum was supplied as infected branches on a screen placed over trees. Inoculation techniques resulted in infection levels up to 100%. Results have produced susceptibility ratings for most conifers grown in North America. Variation in resistance by seed sources was found in Scots pine.

Producing Herbicide Tolerant Populus Using Genetic Transformation Mediated by Agrobacterium Tumefaciens C58: A Summary of Recent Research

We tested the hypothesis that genetic transformation mediated by Agrobacterium tumefaciens strain C58 will produce Populus with better than normal tolerance of the herbicide Roundup (glyphosate). The basic strategy was so-called target enzyme protection. Using a binary C58-based vector, T-DNA from two engineered plasmids (pPMG 85/587 or pCGN 1107) was separately inserted into Populus alba x P. grandidentata cv. ‘Crandon.’ Both these plasmids contained a bacterial gene (aroA) that encodes a chimeric 5-enol-pyruvylshikimate-3-phosphate (EPSP) synthase that tolerates Roundup better than normal enzyme. Compared to plasmid pPMG 85/587, pCGN 1107 contained a better gene promoter and added coding to help movement of chimeric EPSP synthase from cytoplasm to chloroplasts. Transformations with plasmid pPMG 85/587 yielded normal greenhouse plants with aroA and increased Roundup tolerance. This was the first transformation and regeneration of a woody plant with an important gene. Southern blots of greenhouse plants from tissues transformed with pCGN 1107 also showed that aroA was present; hence, plants were produced wherein chimeric EPSP synthase was targeted for chloroplast expression. Roundup tolerance tests of those plants are underway. A host range study revealed that C58 transforms Populus of diverse ancestry. But, parental genotype governs whether a progeny is susceptible or resistant to C58.

Strategic planning for applying biotechnology to woody plant genetics and breeding

Biotechnology can be used to produce products or knowledge, or both (e.g. [22]). But biotechnology means different things to different people. There are the so-called old biotechnologies of, for instance, vegetative propagation, and genetic selection and breeding. Indeed, ‘casual’ vegetative propagation and breeding are about as old as agriculture, and have been systematized for centuries [10,44]. There are also what are collectively termed the new biotechnologies, for example, recombinant DNA (e.g., genetic engineering, gene mapping); somaclonal in vitro genetic selection; in vitro embryo rescue; in vitro sexual hybridization; in vitro somatic cellular hybridization; in vitro vegetative propagation (i.e., micropropagation, micrografting); and in vitro production of haploid, aneuploid, or polyploid plants. However, like other technologies, the new biotechnologies have past histories. For example, protoplast fusion was first achieved 56 years ago [33] and is the basis of somatic cellular hybridization.